The present invention relates generally to computed tomograph (CT) imaging and, more particularly, to a x-ray source utilized in connection with CT systems.
In at least some computed tomograph (CT) imaging system configurations, an x-ray source projects a fan-shaped beam which is collimated to lie within an X-Y plane of a Cartesian coordinate system and generally referred to as the xe2x80x9cimaging planexe2x80x9d. The x-ray beam passes through the object being imaged, such as a patient. The beam, after being attenuated by the object, impinges upon an array of radiation detectors. The intensity of the attenuated beam radiation received at the detector array is dependent upon the attenuation of the x-ray beam by the object. Each detector element of the array produces a separate electrical signal that is a measurement of the beam attenuation at the detector location. The attenuation measurements from all the detectors are acquired separately to produce a transmission profile.
In known third generation CT systems, the x-ray source and the detector array are rotated with a gantry within the imaging plane and around the object to be imaged so that the angle at which the x-ray beam intersects the object constantly changes. X-ray sources typically include x-ray tubes, which emit the x-ray beam at a focal spot. X-ray detectors typically include a collimator for collimating x-ray beams received at the detector. A scintillator is located adjacent the collimator, and photodiodes are positioned adjacent the scintillator.
Multislice CT systems are used to obtain data for an increased number of slices during a scan. Known multislice systems typically include detectors generally known as 3-D detectors. With such 3-D detectors, a plurality of detector elements form separate channels arranged in columns and rows. Each row of detectors forms a separate slice. For example, a two slice detector has two rows of detector elements, and a four slice detector has four rows of detector elements. During a multislice scan, multiple rows of detector cells are simultaneously impinged by the x-ray beam, and therefore data for several slices is obtained.
A system that does not require a rotating x-ray source is described in U.S. Pat. Nos. 4,521,900 and 4,521,901. In the ""900 patent, a large vacuum chamber is used which incorporates an electron gun and ring-shaped targets to produce x-rays. The electron beam emerges from the gun several feet away from the patient, travels a bent path to move toward the targets then hits the material to produce x-rays. The single fairly high power electron beam sweeps out a circle, a ring that surrounds the patient, to produce the xe2x80x9cscanxe2x80x9d effect. One drawback to such a system is that a large vacuum system to enclose the electron beam""s path or trajectory is required, and further, a complicated beam deflection system is employed to accurately steer the beam.
Accordingly, it would be desirable to provide a CT scanner and CT scanner system that provides a x-ray source that reduces the complexity of the scanning system and does not require a rotating x-ray source.
It is therefore one object of the invention to provide a solid state x-ray tube to reduce the complexity of the x-ray tube. In one aspect of the invention, a CT system comprises a solid state x-ray source for a computed tomograph (CT) imaging system is illustrated. X-ray source has a cathode which is preferably formed of a plurality of addressable elements. The cathode is positioned within a vacuum chamber so that electrons emitted thereby impinge upon anode spaced apart from cathode. An electron beam is formed and moves along the length of cathode. The anode is disposed within a cooling block portion and operatively adjacent to an x-ray transmissive window. The anode and x-ray transmissive window are disposed within an elongated channel of the cooling block portion.
Advantageously, the present invention uses cold-cathode technology. The employment of cold-cathode technology allows the possibility for an electron beam source to be turned on and off very quickly with the limitation being the switching speed of the associated electronic and optical circuitry. In addition, fast electronic gating circuits may allow many of these emitting sources to be switched sequentially, thus allowing an electron beam to sweep a target. Such technology will allow the typically rotating x-ray source in a CT system to be removed which substantially removes the complexity associated therewith. For example, bearing issues, target balancing problems, and Z-axis growth problems are associated with prior known CT systems. Also, the prior known systems are complex to service.
Another advantage of the invention is that the use of solid state components eliminates the need for a large vacuum system and a complicated beam deflection system. Other eliminated features compared to the prior art include not requiring a rotating target, a filament heater circuit and motors, and the large support frames associated with a rotating target.
Another advantage of the invention is that because of the fast scan times, applications that require fast scan times such as cardiac imaging may be employed.
Yet another advantage of the invention is that slip rings commonly used in a rotating system may be eliminated. Slip ring connections typically introduce noise and complexity into the transmission of signals obtained from the detectors as well as transmitting power and high voltage to the x-ray source.
Another advantage of the invention is that because of high heat dissipation enabled with a stationary anode, the usual massive target with massive graphite backing is not required to store heat generated by electrons that come to rest in the target. Furthermore, this will greatly reduce or eliminate the need to wait for the X-ray tube to cool.
Another advantage of the invention is that shielding necessary for canceling the effect of the earth""s magnetic field is not required.
Other objects and advantages of the present invention will become apparent upon the following detailed description and appended claims, and upon reference to the accompanying drawings.